Electrical connector pairs are commonly used in electronic equipment. Each pair functions to connect and route electrical signals between different PCBs. A typical connector pair consists of a plug, or header, and a receptacle, each including a plastic housing and multiple contact elements. The complimentary shaped plug and receptacle fit together, such that the electrical contacts of the plug are aligned with the electrical contacts of the receptacle. Each contact is provided with a tail portion that extends beyond the plastic housing to engage, for example, a plated through hole in the PCB. The plug and receptacle are attached to separate PCBs, such that the tail portions of each connector make contact with conductive traces formed on or in each PCB. In this manner, a connector pair completes an electrical circuit between the two PCBs. For instance, these type connectors have been used to electrically connect a daughterboard to another daughterboard, to a backplane board, or to other electrical circuitry. In a typical configuration, the receptacle is connected to the daughterboard while the plug is attached to the backplane.
One early limitation in the use of electrical connectors of this type was in maintaining tolerances for the proper alignment of the contact elements of each connector. This problem has been addressed through the development and use of multiple modules in a single connector. Since each individual module is smaller in size than the entire connector and plastic housing, it is easier to maintain manufacturing tolerances within acceptable limits, thereby ensuring that the plug and receptacle elements fit together properly and that the contacts establish an acceptable electrical connection.
The current United States industry standard for a two part modular connector system for electrically coupling a backplane to a daughter board is set out in specification EIA/IS-64 from the Electronic Industries Association. This specification delineates parameters for 2 mm, two part connectors for use with PCBs and backplanes. The international standard for these two part connectors is set out in IEC 1076-4-001 specification 48B.38.1. Both of these specifications define a free board (daughter board) connector that contains receptacle contacts and a fixed board (backplane or mother board) connector that contains pin contacts. The connector half containing receptacle contacts is commonly referred to as a socket connector, and the connector half containing pin contacts is commonly referred to as a header connector.
The use of stiffeners to help hold the individual connector modules together is known to maintain the correct tolerances and alignment between modules, and to help reduce bowing of the PCB. Alignment problems usually result from a difference in thermal expansion between the materials used in the modules and the PCB. When the assembly is heated during a soldering operation, the thermoplastic housing material of the connector can expand at a faster rate than the PCB material. A typical PCB is made from a composite of fiberglass/epoxy resin and contains copper traces with plated through holes or pads. Built-in residual stresses from the connector manufacturing and assembly processes are released by the heat generated during this soldering process. As a result, the components may not return to their original position after they have cooled down. This can result in misalignment of the connector tails when attached by the soldering process. This misalignment causes the more rigid connector housing to pull on the holes of the PCB through the metal contact tails, flexing the less rigid structure of the PCB to the alignment of the connector assembly. The longer the connector, the more this misalignment effect is compounded. The presence of numerous through holes in the PCB also introduces a less rigid area to the PCB which is more prone to flex during loading. Accordingly, stiffeners have become popular in these types of connector assemblies.
Traditional board stiffeners consist of an angled bar, shell, or U-shaped bar. The board stiffener is typically bolted or screwed to the PCB. In other applications, the stiffener is connected to both the connector and the PCB. Stiffeners are usually made from metallic material. These metal stiffeners have a much stronger stiffness when compared to the plastic housing of the connector or the composite material of the PCB. As a consequence, the stiffener helps to reduce the bowing effect. However, these board stiffeners also have several problems or design disadvantages. One such problem is the increased assembly cost.
A design problem resulting from the use of a stiffener is that the stiffener requires valuable board real estate, i.e., space on the PCB. Attempts to solve the space problem are disclosed in U.S. Pat. No. 5,492,479 (Ortega) which discloses a stiffener having an L-shaped body wherein one leg of the stiffener abuts an outward edge of the PCB and the other leg abuts a surface of the PCB adjacent to the end edge. This stiffener addresses the problem of conserving real estate on the surface of the PCB due to the fact that the stiffener leg is adapted to be attached under the connectors and not behind or adjacent to the connectors. The resulting connector/stiffener assembly is then secured to the PCB using traditional methods.
Another attempt to solve the problem of conserving PCB real estate can be seen in U.S. Pat. No. 5,672,064 (Provencher et al.) which illustrates the use of a stiffener and mounting blocks. Connector modules are held rigidly to the stiffener by the use of slots on one surface of the modules, which slots are adapted to receive barbs formed on the stiffener and hubs on the other surface of the connector which hubs are adapted to be press fit into holes in the stiffener. This design also attempts to solve the problem of conserving real estate by having a stiffener in which no significant surface of the stiffener comes into contact with or abuts the PCB surface. The resulting connector/stiffener assembly is then secured to the PCB using traditional methods.
However, since both of the prior stiffeners are still attached to the PCB in the traditional manner of bolting or screwing, surface area on the PCB is still required to provide stiffener mounting holes as a means of attaching the stiffener to the PCB. This again requires valuable PCB real estate and also creates trace routing problems because the traces running from the edge of the board have to be routed around the stiffener mounting holes.
Accordingly, a need still exists for providing means of connecting together and holding down various connectors, and of providing a means of stiffening the PCB to prevent bowing while minimizing the usage of space on the PCB.